Numerous plugs are known for performing this function. Most of them are of a shape that is designed to prevent the plug from being expelled or from disappearing into the lacrimal canaliculus. For this purpose, practically all plugs have a top collar which is preferably inclined relative to the general axis of the plug in order to bear against the edges of the meatus and thus constitute means for preventing the plug disappearing into the canaliculus, and also an enlarged portion remote from the collar forming anti-expulsion means.
The drawbacks of known plugs lie in the fact that their shapes do not comply with the natural anatomic shapes of lacrimal canaliculi and constitute sources of trauma to tissues adjacent to such canaliculi.